Present-day Internet communications represent the synthesis of technical developments begun in the 1960s. During that time period, the Defense Department developed a communication system to support communications between different United States military computer networks, and later a similar system was used to support the communication between research computer networks at United States universities. These technological developments would subsequently revolutionize the world by forming the basic elements of the Internet.
The Internet
The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, Defense Department officials wanted to connect different types of military computer networks. These different computer networks could not communicate with each other because they used different types of operating systems or networking protocols.
While the Defense Department officials wanted a system that would permit communication between these different computer networks, they realized that a centralized interface system would be vulnerable to missile attacks and sabotage. To avoid this vulnerability, the Defense Department required that the interface system be decentralized with no vulnerable failure points.
The Defense Department developed an interface protocol for communication between these different network computers. A few years later, the National Science Foundation (NSF) wanted to connect different types of network computers located at research institutions across the country. The NSF adopted the Defense Department's interface protocol for communication between these research computer networks. Ultimately, this combination of research computer networks would form the foundation for today's Internet.
Internet Protocols
The Defense Department's interface protocol was called the Internet Protocol (IP) standard. The IP standard now supports communications between computers and networks on the Internet. The IP standard identifies the types of services to be provided to users, and specifies the mechanisms needed to support these services. The IP standard also describes the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the system.
One basic rule governing communications on the Internet is the requirement that a computer user does not need to get involved with details of each communication. In order to accomplish this goal, the IP standard imposes a layered communications structure. All the layers are located on each computer in the network, and each module or layer is a separate component that theoretically functions independent of the other layers.
Two types of transmission protocols may operate with the IP protocol—the Transmission Control Protocol (TCP) or the User Datagram protocol (UDP). TCP was developed to provide connection-oriented, end-to-end data transmission between packet-switched computer networks, and UDP supports a connection-less transmission between computer networks. Unlike UDP, TCP provides certain error recovery and data-checking services. The combination of TCP or UDP with the IP protocol forms a suite of protocols for communication between computers on the Internet.
This suite of protocols form a standardized system for defining how data should be processed, transmitted and received on the Internet. These protocols also define the network communication process, and more importantly, defines how a unit of data should look and what information an information packet message should contain so that the receiving computer can receive the information message and interpret it properly.
Routing
Routers are used to regulate the flow of data through a computer network. A router interprets the logical address of an information packet, such as an IP address, and directs the information packet to its intended destination. Information packets addressed between computers on the same network are not allowed to pass outside the network, while information packets addressed to a computer outside the network are allowed to pass to that computer on the outside network.
A routing table possesses sufficient information for a router to make a determination on whether to accept the communicated information packet on behalf of a destination computer or pass the information packet onto another router on the network. The routing table also permits the router to determine where the information should be forwarded within the network. A Visitor Location Register (VLR) and Home Location Register (HLR) are two examples of such routers. A routing table can be configured manually with routing table entries or dynamically according to changing network topologies—network architecture, network structure, layout of routers, and interconnections between hosts and routers.
Authenticate, Authorize and Accounting (“AAA”)
In an IP-based mobile communications system, the mobile communication device (e.g. cellular phone, pager, etc.) can be generically called a mobile node. Typically, a mobile node changes its point of attachment to the network while maintaining connectivity to its home network. That is, a home network continues to transmit information packets to the mobile node even when the mobile node is located on another network, sometimes referred to as a foreign network. While the mobile node is coupled to the foreign network, the mobile node will be assigned an IP address for the transmission of information packets.
When a mobile node is operating on a foreign network, specialized servers must authenticate, authorize and collect accounting information for services rendered to the mobile node. This authentication, authorization, and accounting activity is called “AAA”, and AAA servers on the home and foreign network perform the AAA activities.
Authentication is the process of proving someone's claimed identity, and security systems on a mobile IP network will often require authentication of the system user's identity before authorizing a requested activity. The AAA server authenticates the identity of an authorized user, and authorizes the mobile node's requested activity. Additionally, the AAA server will also provide the accounting function including tracking usage and charges for use of the network.
A mobile node is assigned an IP address while it conducts a communication session on the foreign network. When a mobile node roams through a foreign network, the wireless connection of the mobile node to the foreign network may transition from one base station (or packet control function) to another. When the transition of the wireless connection occurs, certain prior art protocols send accounting messages to the AAA server that initiate the deallocation of the mobile node's IP address. This deallocation of the IP address may be unintentional because the mobile node intends to continue its communication session while it roams the network. When the deallocation of the IP address occurs, information packets addressed to the mobile node may be misdirected or lost. Other problems, such as billing and accounting difficulties, may be encountered after a premature deallocation of the IP address.